Soil sampling in Houston's greater Fifth Ward reveals toxic levels of lead in yards, play areas

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Houston, like many American cities, has areas with soil contaminated by non-biodegradable and persistent pollutants such as arsenic, lead, nickel and cadmium, known as heavy metals and metalloids. These are both naturally occurring in the atmosphere and a byproduct of industrial metal processing, leaching or runoff and are commonly found in traffic emissions and paint.

While some heavy metals and metalloids—notably zinc and copper—are vital to human health in minute quantities, prolonged exposure is known to cause cognitive decline, organ damage, various cancers and other health problems. Children, especially those in urban areas, are thought to be particularly at risk.

Now, a study led by researchers from the Texas A&M University School of Public Health, with participation by local residents, has found significantly elevated levels of heavy metal contaminants in an area of the Greater Fifth Ward neighborhood two miles northeast of Downtown Houston.

"Heavy metals and metalloids have been extensively studied and regulated over the past 50 years, but evidence is growing that contact is more prevalent than previously thought, especially in so-called cancer clusters like the Greater Fifth Ward, where most residents are socioeconomically disadvantaged racial and ethnic minorities," said Dr. Garett Sansom.

Sansom is with the Department of Environmental and Occupational Health at the Texas A&M School of Public Health and is a corresponding author of the study published in the Journal of Exposure Science & Environmental Epidemiology.

Partnering with residents

The team formed partnerships with Houston-based environmental action groups Coalition of Community Organizations and IMPACT GFW a year before the project began. From these organizations, they recruited five Greater Fifth Ward residents who served as block captains during the study, based on a program coordinated by the Houston Health Department. The five teams consisted of a block captain and Texas A&M students, with at least one member who spoke Spanish.

"A major strength of this study was that residents helped design the study, collect soil samples and share the results," said Sansom. "This made the project a true partnership, with each side benefiting from increased communication and gaining tools that could lead to policy changes and other improvements."

From July to November 2021, after receiving in-person training and related resources, the teams conducted 12 sampling activities for a total of 193 soil samples from residential yards in the Greater Fifth Ward. After being freeze-dried and homogenized, the soil samples were sent to nationally accredited, Houston-based A&B Labs for batch analysis on the type and concentration of arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver.

The researchers then used statistical analyses and screening levels and benchmarks set by the U.S. Environmental Protection Agency to calculate cumulative cancer and non-cancer risks for children and adults, as well as soil suitability for crop growing and related uses.

Results

The highest detectable concentrations of heavy metals were lead, barium and chromium. All samples except for lead had less than or the same levels expected for an urban area.

"The median levels of lead detected in seven samples from play areas (400 mg/kg) and three samples from residential areas (1,200 mg/kg) were four times the levels for Texas overall," said Sansom. "And these likely were underestimated because they did not account for lead-based paint or automotive fuel."

Greater Fifth Ward residents learned of the study results through a mailing and a town hall. Before that, the block captains reviewed and approved the results to ensure that the information was understandable. In addition, a final report was shared with the two community organizations involved.

"This study provided a baseline that could aid the development of environmental protection programs," Sansom said. "In addition, the involvement of community partners was critical to its success and should be used as a model for future research with vulnerable populations and other direct stakeholders."

More information: Leanne S. Fawkes et al, Human health risk assessment of heavy metals in residential soil—Houston, Texas, Journal of Exposure Science & Environmental Epidemiology (2024). DOI: 10.1038/s41370-024-00713-7

Provided by Texas A&M University